• KIEAE Journal
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• 제16권1호
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• pp.5-10
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• 2016

Purpose: The energy consumption in buildings has continuously increased in some countries and it reaches almost 25% of the total energy use in korea. Therefore there are various efforts to minimize energy consumption in buildings, and the regulations on building envelope insulation have been tightened up gradually. To satisfy the building regulation, the use of vacuum insulation panels(VIPs) is increasing. VIP is a high performance insulation materials, so that it can be thinner than conventional insulation material. When VIP is applied in a building, it may cause thermal bridge, which occurs due to very low thermal conductivity compared to other building materials and the envelope of VIPs. Method: This study designed the capsulized VIPs using conventional insulation for reduction of the thermal bridge. Then designed VIPs were applied to a wall. The linear thermal transmittance and the effective thermal conductivity were analyzed by HEAT2 simulation program for two dimensional steady-state heat transfer. The result compared with a wall with non-capsulized VIPs. Result: It analyzed that the wall with capsulized VIPs had lower linear thermal transmittance and reduced the difference of the effective thermal transmittance with one dimensional thermal transmittance compared to that of the wall with non-capsulized VIPs.

• 산업기술연구
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• 제31권B호
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• pp.27-36
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• 2011

In this paper, the applicability of cement grout has been studied as an alternative to bentonite grout for backfill ground heat exchangers. To provide an optimal mixture design, the thermal conductivity of cement grout and bentonite grout with various mixture ratios were experimentally evaluated and compared. Numerical analyses using Fluent(FVM program) were applied to compare the thermal transfer efficiency of the cement grout with that of the bentonite grout used in the construction. Also the effective ground thermal conductivity was measured by In-situ thermal response test. The results showed that the thermal efficiency of the cement grout was better than the bentonite grout. Consequently, the cement grout could be an alternative with more thermal efficiency to bentonite grout for ground heat exchangers.

• 한국태양에너지학회 논문집
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• 제32권5호
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• pp.68-74
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• 2012

Investigation of the effective soil thermal conductivity($k$) is the first step in designing the ground loop heat exchanger(borehole) of a geothermal heat pump system. Another important factor is the borehole thermal resistance($R_b$). Thermal response tests offer a good method to determine the ground thermal properties for the total heat transport in the ground. The first step is measured for initial soil temperature. This is done by supplying a only pump power into a borehole heat exchanger. They need to supply into water unload heat power more than 30 minutes. In this study, the initial soil temperature was found to analysis $14.1{\sim}16.0^{\circ}C$,the ratio was 68.7% represented. In this case of $k$, was 2.1~3.0 $W/m{\cdot}k$, $R_b$ was 0.11~0.20 $m{\cdot}K/W$. In this work, it is also shown that the distribution of a soil thermal conductivity and borehole thermal resistance were on the influence of initial soil temperature. And soil thermal conductivity was related with factors of equation by linear least square method, borehole thermal resistance was on the influence of composite factors.

• 한국재료학회지
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• 제30권2호
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• pp.93-98
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• 2020

Effective control of the heat generated from electronics and semiconductor devices requires a high thermal conductivity and a low thermal expansion coefficient appropriate for devices or modules. A method of reducing the thermal expansion coefficient of Cu has been suggested wherein a ceramic filler having a low thermal expansion coefficient is applied to Cu, which has high thermal conductivity. In this study, using pressureless sintering rather than costly pressure sintering, a polymer solution synthesis method was used to make nano-sized Cu powder for application to Cu matrix with an AlN filler. Due to the low sinterability, the sintered Cu prepared from commercial Cu powder included large pores inside the sintered bodies. A sintered Cu body with Zn, as a liquid phase sintering agent, was prepared by the polymer solution synthesis method for exclusion of pores, which affect thermal conductivity and thermal expansion. The pressureless sintered Cu bodies including Zn showed higher thermal conductivity (180 W/m·K) and lower thermal expansion coefficient (15.8×10^-6/℃) than did the monolithic synthesized Cu sintered body.

• Composites Research
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• 제15권5호
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• pp.27-34
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• 2002

본 연구의 목적은 (주)한국와이바의 CF3327 평직 복합재료의 열전도도를 실험적으로 계측하고 이를 이론적인 예측과 비교하는데 있다. 열전도도 계측을 위하여 비교계측법의 원리를 이용한 실험 장치를 제작하였으며 열전도도가 잘 알려진 그라파이트를 실험함으로써 장비의 정확성을 확인하였다. 미시역학적인 방법은 섬유 및 기지의 물성, 섬유체적비, 직조 형태 등의 변수들이 복합재료의 유효물성치에 미치는 영향을 평가하는데 유용하다. 본 연구에서는 3차원 직-병렬 열저항 개념을 주기적으로 반복되는 평직의 단위구조에 적용하여 열전도도를 예측하였다. 해석 결과를 실험 결과와 비교한 결과 잘 일치함을 확인하였고 섬유체적비가 에폭시 수지 복합재료의 열전도도에 미치는 영향을 고찰하였다.

• 한국태양에너지학회 논문집
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• 제31권4호
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• pp.80-86
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• 2011

Investigation of the effective soil thermal conductivity(k) is the first step in designing the ground loop heat exchanger(borehole) of a geothermal heat pump system. Another important factor is the borehole thermal resistance($R_b$). Thermal response tests offer a good method to determine the ground thermal properties for the total heat transport in the ground. This is done by supplying a constant heat power into a borehole heat exchanger. There are two methods to supply a constant heat power. One is to employ the electricity provided by Korea Electric Power Corporation(KEPCO). The other is to use electricity generated by a generator. In this study, the power supply regulation was found to reduce when the electricity generated by the generator was used. This is because the generator evaluated with the power supply characteristically reduces the power supply regulation between an overload and a complex using. But it sometimes occurs a power supply regulation in In-situ thermal response test. In this case getting of k,$R_b$ requires delay times and restored normal state. However, the effect of the delay times and restored normal state on the soil thermal conductivity and borehole thermal resistance is very small. Therefore it is possible to use a generally accepted delay times and restored normal state in the analysis. In this work, it is also shown that an acceptable range of ${\Delta}k$, ${\Delta}R_b$ for normal state and regulation state might be approximately 0.01-0.16W/m k, and -0.004-0.007m K/W, respectively. Thus, restored normal state of power supply regulation is valuable to recommend.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.186-189
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• 2004

A thermal model of carbon spun yam is presented. The unit cell of spun carbon yam is divided into a number of volume elements and the local material properties have been given to each element. By using Finite Difference Method (FDM), temperature distribution in the unit cell can be obtained. Effective thermal conductivity of the spun carbon yam unit cell is calculated using the temperature distribution and thermal conductivities of local elements.

• 오토저널
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• 제4권3호
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• pp.40-47
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• 1982

Heat transfer on packed bed is considered to be important for the effective designs of chemical reaction equipment, air conditioning system, and storage type heat exchanger, etc. Currently studies are being carried out quite actively in this field in order to increase the heat transfer efficiency. The effect of heat transfer is closely relater to materials, shapes, porosities and packing states of packed bed as well as mutual dimensional relations between particles and the container. Investigation shows that heat transfer results appear to be influenced by such parameters as fluid velocity through packed bed, mass flow, and thermal properties. It is noted that viscosity is also considered to be an important factor in this problem. In this study, effective thermal conductivities on packed bed, effects of thermal conductivity (Ke) and friction factor (Fk) according to change of porosity(.epsilon.) and Reynolds number(Reh(, and pressure loss of the fluid, are experimentally investigated. Results show that the effective thermal conductivity increases and the friction factor decreased, as against the increase of Reynolds number. But as the increase of porosity increase them both.

• 대한기계학회논문집B
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• 제31권9호
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• pp.807-813
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• 2007

Recent research on nanofluids under forced convection experiment shows that there is little relationship between convective heat transfer and thermal conductivity increase of nanofluids. This kind of new findings are totally different from the traditional theory of nanofluids, which says that the higher thermal conductivity is a prerequisite for convective heat transfer enhancement. To elucidate this controversial issue in a very comprehensible manner, simple natural convection experiment has been carried out for the water- and oil-based nanofluids. ($water-Al_2O_3$, transformer $oil-Al_2O_3$) Present research shows that there exists strong dependence between natural convection performance and thermal conductivity increase of nanofluids.

• Journal of Biosystems Engineering
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• 제7권1호
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• pp.1-16
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• 1982

The thermal conductivies of grain are influenced by many physical factors such as' initial temperature, moisture content, composition, bulk density or porosity of grain. However, not only few researchers considered all these factors in determining thermal conductivities of grain but also many researchers considered only moisture content as a major effective factor on the thermal conductivity. This study was conducted to experimentally determine the thermal conductivities of rough rice (3 Japonica-type, 3 Indica-type) and barley(covered, naked) as a function of initial temperature, moisture content and porosity of grain, and to investigate the effect of those physical factors on the thermal conductivities of grain. The results of this study are summarized as follows; 1. The average time correction value for this experimental apparatus was 7 sec, which. was insignificant to the calculated thermal conductivity. The resulting conductivity for considering time correction value was only 4.9 percent higher than that calculated by the non-corrected equation. 2. The thermal conductivity was in the range of 0.1208~0.2058W/$m^{\circ}K$ for naked barley, 0.1138~0.1724W/$m^{\circ}K$ for covered barley, 0.0912~0.1864W/$m^{\circ}K$ for Japonica-type rice and 0.086~0.1774W/$m^{\circ}K$ for Indica-type rice. 3. The thermal conductivities of grain increased with initial temperature and moisture content of grain but decreased with porosity of grain. 4. The regression equations of the thermal conductivity of each grain were determined as a function of initial temperature, moisture content and porosity. The regression equations of the thermal conductivity of both Japonica-type and Indica-type rough rice were also determined.